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PGI Kolloquium:

Prof. Dr. Jonathan Finley,
Technical University of Munich, Germany

PGI Lecture Hall, Building 04.8, 2nd Floor, Room 365

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09.06.2017 11:00 Uhr

Quantum Optics with Semiconductor Nanomaterials

In this talk, I will discuss several research themes pursued in my group in which the photonic and electronic properties of III-V semiconductor nanostructures are tailored to facilitate emergent photonic and quantum technologies.

I will start by discussing experiments in which we use ultrafast optical methods to probe electron spin coherence in individual, optically active quantum dots (QDs). Phenomenological models of electron spin decoherence in optically active quantum dots generally include two basic types of spin relaxation: fast dephasing due to static but randomly distributed hyperfine fields (∼2ns) and a much slower process (>1μs) of irreversible relaxation [1].

Copyright: Prof. Dr. Finley

We will discuss results that show that qubit relaxation is determined by three rather than two distinct stages. The additional stage corresponds to the effect of coherent precession processes that occur in the nuclear spin bath itself, leading to a relatively fast but incomplete non-monotonic relaxation at intermediate timescales (∼750 ns). This behaviour is shown to reflect the interplay between dynamics dominated by the applied magnetic field to one where the quadrupolar interaction within the nuclear spin bath dominates the coherent spin dynamics [2]. By applying correlations in time-distributed pairs of weak optical measurements we directly measure T2∗ and T2 using only repeated projective measurements and without coherent spin control [3,4].

Time permitting, my focus will then move to nanostructures for integrated (quantum) photonics. We will discuss how slow light phenomena in GaAs photonic crystal waveguides can be used to efficiently direct single photons into propagating waveguide modes on a chip [5,6] and illustrate how one can generate, transport and detect quantum light in-situ using integrated NbN superconducting single photon detectors attached to waveguides [7].